2012, Oceanography 25(2):66–79, http://dx.doi.org/10.5670/oceanog.2012.43
Matthew H. Alford | Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, WA, USA
John B. Mickett | Applied Physics Laboratory, University of Washington, Seattle, WA, USA
Shuang Zhang | Applied Physics Laboratory, School of Oceanography, University of Washington, Seattle, WA, USA
Parker MacCready | University of Washington, Seattle, WA, USA
Zhongxiang Zhao | Applied Physics Laboratory, University of Washington, Seattle, WA, USA
Jan Newton | Applied Physics Laboratory, School of Oceanography, University of Washington, Seattle, WA, USA
The low-frequency oceanography of the Washington continental shelf has been studied in great detail over the last several decades owing in part to its high productivity but relatively weak upwelling winds compared to other systems. Interestingly, though many internal wave-resolving measurements have been made, there have been no reports on the region's internal wave climate and the possible feedbacks between internal waves and lower-frequency processes. This paper reports observations over two summers obtained from a new observing system of two moorings and a glider on the Washington continental shelf, with a focus on internal waves and their relationships to lower-frequency currents, stratification, dissolved oxygen, and nutrient distributions. We observe a rich, variable internal wave field that appears to be modulated in part by a coastal jet and its response to the region's frequent wind reversals. The internal wave spectral level at intermediate frequencies is consistent with the model spectrum of Levine (2002) developed for continental shelves. Superimposed on this continuum are (1) a strong but highly temporally variable semidiurnal internal tide field and (2) an energetic field of high-frequency nonlinear internal waves (NLIWs). Mean semidiurnal energy flux is about 80 W m–1 to the north-northeast. The onshore direction of the flux and its lack of a strong spring/neap cycle suggest it is at least partly generated remotely. Nonlinear wave amplitudes reach 38 m in 100 m of water, making them among the strongest observed on continental shelves of similar depth. They often occur each 12.4 hours, clearly linking them to the tide. Like the internal tide energy flux, the NLIWs are also directed toward the north-northeast. However, their phasing is not constant with respect to either the baroclinic or barotropic currents, and their amplitude is uncorrelated with either internal-tide energy flux or barotropic tidal forcing, suggesting substantial modulation by the low-frequency currents and stratification.
Alford, M.H., J.B. Mickett, S. Zhang, P. MacCready, Z. Zhao, and J. Newton. 2012. Internal waves on the Washington continental shelf. Oceanography 25(2):66–79, http://dx.doi.org/10.5670/oceanog.2012.43.
Alford, M.H. 2003. Redistribution of energy available for ocean mixing by long-range propagation of internal waves. Nature 423:159–163, http://dx.doi.org/10.1038/nature01628.
Alford, M.H. 2010. Sustained, full-water-column observations of internal waves and mixing near Mendocino Escarpment. Journal of Physical Oceanography 40(12):2,643–2,660, http://dx.doi.org/10.1175/2010JPO4502.1.
Alford, M.H., M.C. Gregg, and M.A. Merrifield. 2006. Structure, propagation and mixing of energetic baroclinic tides in Mamala Bay, Oahu, Hawaii. Journal of Physical Oceanography 36(6):997–1,018, http://dx.doi.org/10.1175/JPO2877.1.
Alford, M.H., R. Lien, H. Simmons, J.M. Klymak, Y. Yang, D. Tang, and M. Chang. 2010. Speed and evolution of nonlinear internal waves transiting the South China Sea. Journal of Physical Oceanography 40(6):1,338–1,355, http://dx.doi.org/10.1175/2010JPO4388.1.
Alford, M.H., J.A. MacKinnon, J.D. Nash, H.L. Simmons, A. Pickering, J.M. Klymak, R. Pinkel, O. Sun, L. Rainville, R. Musgrave, and others. 2011. Energy flux and dissipation in Luzon Strait: Two tales of two ridges. Journal of Physical Oceanography 41(11):2,211–2,222, http://dx.doi.org/10.1175/JPO-D-11-073.1.
Alford, M.H., and Z. Zhao. 2007a. Global patterns of low-mode internal-wave propagation. Part I: Energy and energy flux. Journal of Physical Oceanography 37(7):1,829–1,848, http://dx.doi.org/10.1175/JPO3085.1.
Alford, M.H., and Z. Zhao. 2007b. Global patterns of low-mode internal-wave propagation. Part II: Group velocity. Journal of Physical Oceanography 37(7):1,849–1,858, http://dx.doi.org/10.1175/JPO3086.1.
Althaus, A., E. Kunze, and T. Sanford. 2003. Internal tide radiation from Mendocino Escarpment. Journal of Physical Oceanography 33(7):1,510–1,527, http://dx.doi.org/10.1175/1520-0485(2003)033<1510:ITRFME>2.0.CO;2.
Apel, J., L. Ostrovsky, Y. Stepanyants, and J. Lynch. 2006. Internal solitons in the ocean. Woods Hole Oceanographic Institution Technical Report, WHOI-2006-04. Available online at: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA450369 (accessed May 15, 2012).
Apel, J.R., J.R. Holbrook, A.K. Liu, and J.J. Tsai. 1985. The Sulu Sea internal soliton experiment. Journal of Physical Oceanography 15:1,625–1,651, http://dx.doi.org/10.1175/1520-0485(1985)015<1625:TSSISE>2.0.CO;2.
Avicola, G.S., J.N. Moum, A. Perlin, and M.D. Levine. 2007. Enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet. Journal of Geophysical Research 112, C06024, http://dx.doi.org/10.1029/2006JC003831.
Bogucki, D., T. Dickey, and L. Redekopp. 1997. Sediment resuspension and mixing by resonantly generated internal solitary waves. Journal of Physical Oceanography 27(7):1,181–1,196, http://dx.doi.org/10.1175/1520-0485(1997)027<1181:SRAMBR>2.0.CO;2.
Butman, B., P. Alexander, A. Scotti, R. Beardsley, and S. Anderson. 2006. Large internal waves in Massachusetts Bay transport sediments offshore. Continental Shelf Research 26:2,029–2,049, http://dx.doi.org/10.1016/j.csr.2006.07.022.
Cairns, J.L., and G.O. Williams. 1976. Internal wave observations from a midwater float, 2. Journal of Geophysical Research 81:1,943–1,950, http://dx.doi.org/10.1029/JC081i012p01943.
Carter, G.S., and M.C. Gregg. 2002. Intense, variable mixing near the head of Monterey Submarine Canyon. Journal of Physical Oceanography 32:3,145–3,165, http://dx.doi.org/10.1175/1520-0485(2002)032<3145:IVMNTH>2.0.CO;2.
Colosi, J.A., R.C. Beardsley, J.F. Lynch, G. Gawarkiewicz, C.S. Chiu, and A. Scotti. 2001. Observations of nonlinear internal waves on the outer New England continental shelf during the summer Shelfbreak Primer Study. Journal of Geophysical Research 106(C5):9,587–9,601, http://dx.doi.org/10.1029/2000JC900124.
D’Asaro, E. 1985. The energy flux from the wind to near-inertial motions in the mixed layer. Journal of Physical Oceanography 15:943–959, http://dx.doi.org/10.1175/1520-0485(1985)015<1043:TEFFTW>2.0.CO;2.
Egbert, G., and S. Erofeeva. 2002. Efficient inverse modeling of barotropic ocean tides. Journal of Atmospheric and Oceanic Technology 19:183–204, http://dx.doi.org/10.1175/1520-0426(2002)019<0183:EIMOBO>2.0.CO;2.
Farmer, D., and L. Armi. 1999. The generation and trapping of solitary waves over topography. Science 283:188–190, http://dx.doi.org/10.1126/science.283.5399.188.
Farmer, D., Q. Li, and J.-H. Park. 2009. Internal wave observations in the South China Sea: The role of rotation and nonlinearity. Atmosphere-Ocean 47:267–280, http://dx.doi.org/10.3137/OC313.2009.
Foreman, M., W. Callendar, A. MacFadyen, B. Hickey, R. Thomson, and E. Di Lorenzo. 2008. Modeling the generation of the Juan de Fuca Eddy. Journal of Geophysical Research 113, C03006, http://dx.doi.org/10.1029/2006JC004082.
Garrett, C.J.R., and W.H. Munk. 1975. Space-time scales of internal waves: A progress report. Journal of Geophysical Research 80(3):291–297, http://dx.doi.org/10.1029/JC080i003p00291.
Gonella, J. 1972. A rotary-component method for analysing meteorological and oceanographic vector time series. Deep-Sea Research 19:833–846, http://dx.doi.org/10.1016/0011-7471(72)90002-2.
Hickey, B.M. 1978. The California Current System: Hypotheses and facts. Progress in Oceanography 8:191–279, http://dx.doi.org/10.1016/0079-6611(79)90002-8.
Hickey, B.M., and N.S. Banas. 2003. Oceanography of the US Pacific Northwest coastal ocean and estuaries with application to coastal ecology. Estuaries 26(4B):1,010–1,031, http://dx.doi.org/10.1007/BF02803360.
Hickey, B.M., and N.S. Banas. 2008. Why is the northern California Current so productive? Oceanography 21(4):90–107, http://dx.doi.org/10.5670/oceanog.2008.07.
Horner, R., D. Garrison, and F. Plumley. 1997. Harmful algal blooms and red tide problems on the US west coast. Limnology and Oceanography 42(5):1,076–1,088, http://dx.doi.org/10.4319/lo.1997.42.5_part_2.1076.
Jackson, C.R., J.C.B. da Silva, and G. Jeans. 2012. The generation of nonlinear internal waves. Oceanography 25(2):108–123, http://dx.doi.org/10.5670/oceanog.2012.46.
Kelly, S., and J.D. Nash. 2010. Internal-tide generation and destruction by shoaling internal tides. Geophysical Research Letters 37, L23611, http://dx.doi.org/10.1029/2010GL045598.
Klymak, J.M., and J.N. Moum. 2003. Internal solitary waves of elevation advancing on a shoaling shelf. Geophysical Research Letters 30(20), 2045, http://dx.doi.org/10.1029/2003GL017706.
Lamb, K. 2002. A numerical investigation of solitary internal waves with trapped cores formed via shoaling. Journal of Fluid Mechanics 451:109–144, http://dx.doi.org/10.1017/S002211200100636X.
Levine, M. 2002. A modification of the Garrett-Munk internal wave spectrum. Journal of Physical Oceanography 32:3,166–3,181, http://dx.doi.org/10.1175/1520-0485(2002)032<3166:AMOTGM>2.0.CO;2.
Lien, R., E.A. D’Asaro, F. Henyey, M. Huei Chang, T.Y. Tang, and Y.-J. Yang. 2012. Trapped core formation within a shoaling nonlinear internal wave. Journal of Physical Oceanography 42(4):511–525, http://dx.doi.org/10.1175/2011JPO4578.1.
Lien, R.-C., T.Y. Tang, M.H. Chang, and E.A. D’Asaro. 2005. Energy of nonlinear internal waves in the South China Sea. Geophysical Research Letters 32, L05615, http://dx.doi.org/10.1029/2004GL022012.
Lighthill, J. 1978. Waves in Fluids. Cambridge University Press, New York, 496 pp.
Lucas, A., P. Franks, and C. Dupont. 2011. Horizontal internal-tide fluxes support elevated phytoplankton productivity over the inner continental shelf. Limnology & Oceanography: Fluids & Environments 1:56–74, http://lofe.dukejournals.org/content/1/56.full.pdf.
MacFadyen, A., and B.M. Hickey. 2010. Generation and evolution of a topographically linked, mesoscale eddy under steady and variable wind-forcing. Continental Shelf Research 30(13):1,387–1,402, http://dx.doi.org/10.1016/j.csr.2010.04.001.
MacKinnon, J.A., and M.C. Gregg. 2003a. Mixing on the late-summer New England Shelf: Solibores, shear, and stratification. Journal of Physical Oceanography 33:1,476–1,492, http://dx.doi.org/10.1175/1520-0485(2003)033<1476:MOTLNE>2.0.CO;2.
MacKinnon, J.A., and M.C. Gregg. 2003b. Shear and baroclinic energy flux on the summer New England Shelf. Journal of Physical Oceanography 33:1,462–1,475, http://dx.doi.org/10.1175/1520-0485(2003)033<1462:SABEFO>2.0.CO;2.
Martini, K.I., M.H. Alford, S. Kelly, and J.D. Nash. 2011. Observations of internal tides on the Oregon continental slope. Journal of Physical Oceanography 41(9):1,772–1,794, http://dx.doi.org/10.1175/2011JPO4581.1.
Martini, K.I., M.H. Alford, S. Kelly, and J.D. Nash. In press. Observations of remotely generated internal tides breaking on the Oregon continental slope. Journal of Physical Oceanography.
Maxworthy, T. 1980. On the formation of nonlinear internal waves from the gravitational collapse of mixed regions in two and three dimensions. Journal of Fluid Mechanics 96(1):47–64, http://dx.doi.org/10.1017/S0022112080002017.
Mooers, C.N.K. 1970. The interaction of an internal tide with the frontal zone in a coastal upwelling region. PhD thesis, Oregon State University.
Nagovitsyn, A., E. Pelinovsky, and Y. Stepanyants. 1991. Observation and analysis of solitary internal waves in the coastal zone of the Sea of Okhotsk. Journal of Physical Oceanography 2(1):65–70, http://dx.doi.org/10.1007/BF02197419.
Nash, J.D., M.H. Alford, and E. Kunze. 2005. Estimating internal-wave energy fluxes in the ocean. Journal of Atmospheric and Oceanic Technology 22(10):1,551–1,570, http://dx.doi.org/10.1175/JTECH1784.1.
Nash, J.D., and J. Moum. 2005. River plumes as a source of large-amplitude internal waves in the coastal ocean. Nature 437:400–403, http://dx.doi.org/10.1038/nature03936.
Nash, J.D., E.L. Shroyer, S.M. Kelly, M.E. Inall, T.F. Duda, M.D. Levine, N.L. Jones, and R.C. Musgrave. 2012. Are any coastal internal tides predictable? Oceanography 25(2):80–95, http://dx.doi.org/10.5670/oceanog.2012.44.
Ostrovsky, L.A., and Y. Stepanyants. 1989. Do internal solitons exist in the ocean? Journal of Geophysical Research 27:2,906–2,926, http://dx.doi.org/10.1029/RG027i003p00293.
Pineda, J. 1999. Circulation and larval distribution in internal tidal bore warm fronts. Limnology and Oceanography 44(6):1,400–1,414, http://dx.doi.org/10.4319/lo.19188.8.131.520.
Pingree, R.D., and A.L. New. 1989. Downward propagation of internal tide energy into the Bay of Biscay. Deep-Sea Research Part I 36(5):735–758, http://dx.doi.org/10.1016/0198-0149(89)90148-9.
Rainville, L., and R. Pinkel. 2006. Propagation of low-mode internal waves through the ocean. Journal of Physical Oceanography 36:1,220–1,236, http://dx.doi.org/10.1175/JPO2889.1.
Ramp, S.R., D. Tang, T.F. Duda, J.F. Lynch, A.K. Liu, C.S. Chiu, F. Bahr, Y.R. Kim, and Y.J. Yang. 2004. Internal solitons in the northeastern South China Sea. Part I: Sources and deep water propagation. IEEE Journal of Oceanic Engineering 29(4):1,157–1,181, http://dx.doi.org/10.1109/JOE.2004.840839.
Riedel, K.S., and A. Sidorenko. 1995. Minimum bias multiple taper spectral estimation. IEEE Transactions on Signal Processing 43(1):188–195, http://dx.doi.org/10.1109/78.365298.
Sabine, C.L., R.A. Feely, N. Gruber, R.M. Key, K. Lee, J.L. Bullister, R. Wanninkhof, C.S. Wong, D.W.R. Wallace, B. Tilbrook, and others. 2004. The oceanic sink for anthropogenic CO2. Science 305:367–371, http://dx.doi.org/10.1126/science.1097403.
Sandstrom, H., and J.A. Elliott. 1984. Internal tide and solitons on the Scotian shelf: A nutrient pump at work. Journal of Geophysical Research 89(C4):6,415–6,426, http://dx.doi.org/10.1029/JC089iC04p06415.
Sandstrom, H., and N.S. Oakey. 1995. Dissipation in internal tides and solitary waves. Journal of Physical Oceanography 25:604–614, http://dx.doi.org/10.1175/1520-0485(1995)025<0604:DIITAS>2.0.CO;2.
Scotti, A., and J. Pineda. 2004. Observation of very large and steep internal waves of elevation near the Massachusetts coast. Geophysical Research Letters 31, L22307, http://dx.doi.org/10.1029/2004GL021052.
Shroyer, E., J. Moum, and J. Nash. 2011. Nonlinear internal waves over New Jersey’s continental shelf. Journal of Geophysical Research 116, C03022, http://dx.doi.org/10.1029/2010JC006332.
St. Laurent, L., and C. Garrett. 2002. The role of internal tides in mixing the deep ocean. Journal of Physical Oceanography 32(10):2,882–2,899, http://dx.doi.org/10.1175/1520-0485(2002)032<2882:TROITI>2.0.CO;2.
St. Laurent, L.C., H.L. Simmons, T.Y. Tang, and Y.H. Wang. 2011. Turbulent properties of internal waves in the South China Sea. Oceanography 24(4):78–87, http://dx.doi.org/10.5670/oceanog.2011.96.
Sutherland, D.A., P. MacCready, N.S. Banas, and L.F. Smedstad. 2011. A model study of the Salish Sea estuarine circulation. Journal of Physical Oceanography 41(6):1,125–1,143, http://dx.doi.org/10.1175/2011JPO4540.1.
Whitney, F.A., H.J. Freeland, and M. Robert. 2008. Persistently declining oxygen levels in the interior waters of the eastern subarctic Pacific. Progress in Oceanography 7(2):179–199, http://dx.doi.org/10.1016/j.pocean.2007.08.007.
Zhao, Z., and M.H. Alford. 2009. New altimetric estimates of mode-one M2 internal tides in the Central North Pacific Ocean. Journal of Physical Oceanography 39:1,669–1,684, http://dx.doi.org/10.1175/2009JPO3922.1.